When I see that I can't prevent myself to think about an option to "named" a mixing configuration and be able to play it using a method like : PlayMixing("mixing_name")

Artist would be able to test and set-up bunch of animation mixings that should be played in specific situation and developer would be able to play those using one line of code instead of playing as much of animation as the mixing contains.

Preview makes the most sense to test transitions. Spine may allow setting up mix durations (for AnimationStateData at runtime) in the editor. Playing back a sequence of animations as you described might be useful in some cases, but I think most games are more dynamic and it's already not hard to queue up animations at runtime. What might make sense for Preview is to press a record button, set up some animations, then stop. This would let you play a complex mixing situation repeatedly. For some mix situations you can set them up by changing the speed to 0 to stop everything, adjust the mix duration for the next transition, click the next animation, then increase the speed and repeat the process for the next transition.

Is there anymore documentation on how you setup preview to view how the animations look back to back? I've been messing around with preview, but it seems to only combine the animations together rather than play one then the other.

Sorry, we don't have documentation yet. To play one animation, then another, you need to play the first, wait, then play the second. In the future we plan to have a record and play button, so you can repeat a sequence.

Very useful feature! Ability to record a sequence sounds great. Ability to play selected animation once instead of looping would be great. Ie i have an idle animation on track 0 and want to play some other stuff on other track(s) once.